As a seat lifter structure applicable to a vehicle seat having a cushion seat and a seat back, a structure as described in the Patent Document 1 has been known.
The seat lifter structure as described in the Patent Document 1 is equipped with a brake unit having a pinion and fixed to a seat mount bracket side that moves up and down, and a sector arranged in parallel to the seat mount bracket and rotates in coordination with its up and down motion, where it is made such that a braking is applied to the up and down motion of the seat mount bracket by engaging in advance a gear provided on the sector with the pinion.
Patent Document 1: Japanese Patent Application Publication No. 2000-255295
In the case where the seat is mounted on a vehicle body of a vehicle, in the conventional seat lifter structure, a gap is provided between the sector and the seat mount bracket that is arranged in parallel on an outer side in a width direction of the vehicle with respect to the sector.
For this reason, when a large force to a rear side is exerted with respect to the seat back, the seat mount bracket is easily approaching to the sector side and deforming such that the gap with the sector arranged on an inner side is filled, and in conjunction with that approaching and deforming, it is expected that the sector is also deformed to the inner side.
When these deformations occur, a relative position of the gear of the sector and the pinion of the brake unit fixed to the seat mount bracket will be displaced, and there is a danger for causing a trouble in a raising/lowering operation of the seat.
Also, in the case where the vehicle is collided from behind, it has been impossible to deny a possibility of causing a fall down of the seat back to a rear side as the deformations of the sector and the seat mount bracket occur excessively due to a large impact load.